Recent years have seen implementation of many surface modification methods, in which, in order to modify surface properties of various particles, these particles are treated with a surface-modifying agent to form a film of surface-modifying agent on the surface of the particles; methods, in other words, of manufacturing surface-modified particles by covering the surface of particles with surface-modifying agent. Methods of manufacturing surface-modified particles include the dry process, kneading methods, stirring methods using a medium (methods of performing surface modification in a liquid phase), methods of performing surface modification in a gaseous phase, the spray-dry method, etc.
For example, Fine Particle Engineering: Fundamentals and Applications of Distribution, (Japan Particle Industry and Technology Association, Ed., Asakura Shoten Co., Ltd., First Ed., First Printing, Jun. 25, 1994), pp. 123-36, discusses a method of manufacturing covered compound particles using a dry-type grinder (such as a high-speed rotation type impact grinder, grinding mill, ball mill, roll mill, medium stirring type grinder, or jet mill) to bond to the surface of particles in the form of a powder a different substance (surface-modifying agent) in the form of a powder, thereby modifying surface properties of the particles.
However, in the foregoing conventional particle-modifying method, surface modification processing causes the particles to become electrically charged, which makes it difficult to handle the particles thereafter. Moreover, an extremely long time is required for surface modification processing. A further problem is that the operations of surface modification processing are complicated, and require an expensive device. In addition, the foregoing particle modification method was unable to obtain spherical modified particles of uniform diameter which contain a polymer or are covered with a polymer film.
Another method similar to the foregoing method of manufacturing surface-modified particles is one in which the surface of particles is covered by condensing a vapor thereon, thus increasing the size of the particles. Methods of this type include, for example, a method of collecting dust particles using the dust collecting device disclosed in Japanese Unexamined Patent Publication No. 52-9182/1977 (Tokukaisho 52-9182), and the particle measurement method disclosed in Japanese Unexamined Patent Publication No. 62-225926/1987 (Tokukaisho 62-225926). A similar method is also disclosed in Japanese Unexamined Patent Publication No. 7-83820/1995 (Tokukaihei 7-83820). With each of the foregoing methods, spherical shape-modified particles of substantially uniform size can be obtained.
Further, since the chief object of the methods disclosed in each of the foregoing publications is simply to increase the particle diameter, substances such as water and alcohol, which are liquid at room temperature, are used as the vapor.
Further, EP 0 794 017 A2 discloses a method of forming a film of surface-modifying agent on the surface of particles by exposing them to a super-saturated atmosphere of the surface-modifying agent for modifying surface properties of the particles, causing the surface-modifying agent to condense on the surface of the particles.
However, the surface-modifying agent is vaporized in each of the foregoing methods; none of them gives any particular thought to forming on the surface of the particles a surface-modifying agent which is solid at room temperature and atmospheric pressure. This leads to the problem of limitation of the materials which can be used, because materials which do not vaporize, such as resins (polymers), cannot be used.
In this way, the foregoing conventional methods are unable to perform surface treating of particles using a surface-modifying agent which is solid at room temperature and atmospheric pressure, without electrically charging the particles, using a simple device and operations, and in a short time. For this reason, a method of manufacturing modified particles which is capable of performing surface modification of particles with a surface-modifying agent which is solid at room temperature and atmospheric pressure is called for, as is a manufacturing device for use therein.